1. Field of the Invention
The present invention relates to particle screens, and more particularly, to rotary screens of the type which includes inclined screen plates and a dust pan which are driven as a unit in a gyratory path by means of an eccentric drive.
2. Prior Art
A variety of screening devices are presently available for sorting different particles into various size ranges for subsequent use, such as in the making of paper, the manufacture of particle board in the food industry for screening rice and in the rock industry for screening asbestos and asbestos fibers. These screening devices generally consist of screening surfaces which are inclined in one plane and agitated by a proper mechanical motion. The characteristics of the screen motion are selected for the best combination of material conveying abilities and particle size separation efficiencies.
However, such screens often become clogged. For example, in screening wood particles, wet, sticky sawdust particles may clog the screen, and particularly in cold weather when these particles tend to freeze to the surface of the screen, clogging of the screen results with reduced screening efficiency. Often the result is that the screens must be temporarily shut down and cleaned by hand at frequent intervals.
One approach to this problem has been to support trays of balls in the screen assembly which randomly impact the bottom of the screening surfaces during movement thereof. Screen assemblies of this type are generally composed of a rectangular frame structure with a plurality of cross braces extending through the open central region of the frame structure, with a screen of the desired mesh attached to the top of the frame structure, supported by the cross braces.
The balls are then placed within the rectangular openings formed by the cross braces and the outside frame structure and a latticework having sufficiently small openings tp prevent the balls from passing through it is secured to the bottom of the frame. The balls are thus contained in the compartments formed by the rectangular openings, screen and latticework and, theoretically, engage the bottom surface of the screen when they bounce due to the motion of the screen assembly. An example of a device of this type is illustrated in Simpson U.S. Pat. No. 2,114,406.
Although effective under normal operating conditions, this type of anti-clogging device is not sufficient to prevent operating problems under more severe conditions. Wet or otherwise sticky particles tend to build up inside the ball compartments, thus restricting the mobility of the balls to the point where they become ineffective. The ball compartments then quickly fill up with sticky particles and the screening apparatus ceases to function.